A typical Transcranial Magnetic Stimulation (TMS) electromagnet includes a pair of coils that are joined to form a flat figure-8 shaped electromagnet. Such figure-eight double coil magnets are well known, for instance the 70 mm double-coil configuration from Magstim (e.g., Model 9925, Magstim Ltd., Wales, UK). The electromagnets can be powered by commercially available power sources such as the “Magstim Rapid2” (Magstim Ltd., Wales, UK) that provides electrical currents for pulsed magnetic fields. The magnetic field projected from standard figure-8 shaped double coil electromagnets is not optimal for deep brain stimulation, however. In particular, the depth and shape of the emitted field is limited.
For conventional circular and double circular coils, the Biot-Savart law dictates that magnetic field strength declines as a function of distance from face of a coil. This makes focal stimulation of the brain challenging to achieve at the cortical surface (beneath scalp, skull and meninges), and even more difficult beneath the cortical surface.
Alternative configurations for TMS electromagnets have been proposed, including those described in Zangen et al. (U.S. Patent applications publication Nos. 2006/0287566 and 2004/0078056). Alternative designs have likewise been proposed in Levkovitz Y, Roth Y, Harel EV, Braw Y, Sheer A, Zangen A, “A randomized controlled feasibility and safety study of deep transcranial magnetic stimulation.” Clin. Neurophysiol. 118(12):2730-44 (December 2007).
However, the proposed designs described above each have substantial disadvantages, particularly with regard to the specificity and control of the magnetic field generated, as well as the ease with which these magnets may be fabricated and characterized. Described herein are TMS electromagnets configured to address many of the problems described above. In particular, the inventors have found that, unexpectedly, TMS electromagnets formed from coils that are not linear, but are instead curved or bent to form a “V”, “U” or “Y” may result in magnetic field intensities that are well suited for deep-brain TMS.
The coils described herein for TMS may therefore be designed to accommodate a difficult balance between focality, and power level delivered to a target. This balance has been particularly difficult to achieve with known TMS electromagnets, yet is of great importance when the target is below the cortical surface of the brain.
Examples of systems, devices and methods that may benefit from the TMS coils described herein may be found, for example, in any of the following applications: Patent Application No. PCT/US2008/071663, (titled “DEVICE AND METHOD FOR TREATING HYPERTENSION VIA NON-INVASIVE NEUROMODULATION”) filed Jul. 30, 2008; Patent Application No. PCT/US2008/072930, (titled “GANTRY AND SWITCHES FOR POSITION-BASED TRIGGERING OF TMS PULSES IN MOVING COILS”) filed Aug. 12, 2008; Patent Application No. PCT/US2008/073751, (titled “FIRING PATTERNS FOR DEEP BRAIN TRANSCRANIAL MAGNETIC STIMULATION”), filed Aug. 20, 2008; Patent Application No. PCT/US2008/075575 (titled “FOCUSING MAGNETIC FIELDS WITH ATTRACTOR MAGNETS AND CONCENTRATOR DEVICES”), filed Sep. 8, 2008; Patent Application No. PCT/US2008/075583 (titled “PITCH, ROLL, AND YAW MOTIONS FOR ELECTROMAGNET ARRAYS”), filed Sep. 8, 2008; Patent Application No. PCT/US2008/075706 (titled “FOCUSED MAGNETIC FIELDS”), filed Sep. 9, 2008; Patent Application No. PCT/US2008/075824 (titled “AUTOMATED MOVEMENT OF ELECTROMAGNETS TRACKING ECCENTRICITY OF THE HEAD”), filed Sep. 10, 2008; Patent Application No. PCT/US2008/077851 (titled “SYSTEMS AND METHODS FOR COOLING ELECTROMAGNETS FOR TRANSCRANIAL MAGNETIC STIMULATION”), filed Sep. 26, 2008; Patent Application No. PCT/US2008/079378 (titled “DISPLAY OF MODELED MAGNETIC FIELDS”), filed Oct. 9, 2008; Patent Application No. PCT/US2008/081048 (titled “INTRA-SESSION CONTROL OF TRANSCRANIAL MAGNETIC STIMULATION”), filed Oct. 24, 2008; Patent Application No. PCT/US2008/081307 (titled “TRANSCRANIAL MAGNETIC STIMULATION WITH PROTECTION OF MAGNET-ADJACENT STRUCTURES”), filed Oct. 27, 2008; U.S. patent application Ser. No. 12/324,227 (titled “TRANSCRANIAL MAGNETIC STIMULATION OF DEEP BRAIN TARGETS”), filed Nov. 26, 2008; U.S. patent application Ser. No. 12/185,544 (titled “MONOPHASIC MULTI-COIL ARRAYS FOR TRANCRANIAL MAGNETIC STIMULATION”), filed Aug. 4, 2008; and Patent Application No. PCT/US2008/072154 (titled “MONOPHASIC MULTI-COIL ARRAYS FOR TRANSCRANIAL MAGNETIC STIMULATION”), filed Aug. 4, 2008.